Stuffer crimper with driven choke members for pressure control in the crimping zone

ABSTRACT

A stuffer crimper fed with yarn from a pair of feed rolls having a chamber defining a crimping zone adjacent the feed rolls followed in succession by a heating zone and a cooling zone where the pressure on the yarn core within said crimping zone and the pressure on the core passing through the succeeding heating and cooling zones are independently controlled by roller means having core gripping surfacing projecting into said chamber at the juncture of said crimping and heating zones, said roller means being mounted and driven to rotate parallel to the axes of said feed rolls at a speed related to the speed of said feed rolls.

[ 51 Dec. 26, 1972 United States Patent Trifunovic [s41 STUFFER CRIMPER WITH DRIVEN 3,046,633 7/1962 Ohuhi a s CHOKE MEMBERS FOR PRESSURE 3,090,096 5/1963 Schwartz.................................28/1.6 CONTROL IN TH CRIMPING ZONE 3,417,447 12/1968 Trifunovic et a1. ..................28/l.6 X

[72] Inventor: Alexander L. 'lriiunovlc, Wilmington, Del.

Assignee: Joseph Bancroft 8: Sons Company,

Primary Examiner-Louis K. Rimrodt Attorney-Birch, Swindler, McKie & Beckett Wilmington, Del. ABSTRACT Much 2 1971 A stuffer crimper fed with yarn from a pair of feed [2]] Appl. No.: 128,363

22 F'l d: l l rolls having a chamber defining a crimping zone adjacent the feed rolls followed in succession by a heating zone and a cooling zone where the pressure on the yarn core within said crimping zone and the pressure on the core passing through the succeeding heating and cooling zones are independently controlled by roller means having core gripping surfacing projecting into said chamber at the juncture of said crimping and Ju l w 2: "2 1 06 m u .l 8 m L m... C Su UIF .l. l.:. 2 00 555 [ll heating zones, said roller means being mounted and driven to rotate parallel to the axes of said feed rolls at a speed related to the speed of said feed rolls.

[56] References Cited UNITED STATES PATENTS 2,575,839 llll9$l Rainard........................ 3,027,619 4/1962 List et 11 Claims, 2 Drawing Figures PATENTED DEC 2 s 1912 ATTORNEYS STUFFER CRIMPER WITH DRIVEN CHOKE MEMBERS FOR PRESSURE CONTROL IN THE CRIMPING ZONE GENERAL BACKGROUND OF THE INVENTION This invention is generally concerned with yarn crimping apparatus and, particularly, relates to stuffer crimpers of the type wherein a yarn is fed between feed rolls into one end of a chamber to form a core of crimped yarn which is advanced through the chamber by the pressure and build up of crimped yarn introduced by the feed rolls. More specifically, this invention is concerned with a stuffer crimper fed with yarn from a pair of feed rolls where the chamber through which the core of crimped yarn passes defines a crimping zone adjacent the feed rolls followed in succession by a heating zone and a cooling zone and is directed to obtaining independent control of the pressure on the core passing through the crimping zone relative to the pressure on the core passing through the succeeding heating and cooling zones.

in the prior art of yarn crimping utilizing stufi'er crimper apparatus, effort has been directed to achieving uniformity in the crimping action and also toward obtaining optimum control, as desired for different yarn end uses, of the leg length for the yarn crimps. Depending upon the use to which the crimped yarn product is to be put, longer or shorter crimp leg lengths are desired. Also, control of the sharpness of the bend or crimp to obtain the desired bulk for the crimped yarn product has been an objective in prior stuffer crimper developments. For example, in the heavier denier yarns which find particular application as carpet yarns, the achievement of a long leg length for the yarn crimps and a sharp angle between the successive legs in the crimped yarn is desirable for optimum bulk and results when the yarn is incorporated in the finished carpet. The problem has been in being able to successfully and reliably, with repeatability, obtain control of the crimp leg length and crimp angle in yarn.

lt is a principal object of the instant invention to provide a stuffer crimper wherein effective independent control of the pressures applied to the yarn core in the crimping zone relative to that in the heating and cooling zones can be achieved.

it is a further important object of this invention to provide yarn crimping apparatus wherein precise control of the pressure imparted to the yarn core in the crimping zone of a stuffer crimper chamber, immediately above the feed rolls, can be obtained and this pressure rendered independent of the frictional or other back pressure to which the core is exposed in passing through the subsequent heating and cooling zones of the stuffer crimper chamber.

Another object of this invention is to provide positively driven roller means at the outlet of the crimping zone, adjacent the feed rolls which introduce yarn to the stuffer crimper chamber, to control the pressure on the core within the crimping zone by such roller means being driven in relation to the yarn feed speed and being rotated parallel to the axes of the feed rolls.

A further object of the invention is to provide a stuffer crimper having a yarn core confining chamber including crimping, heating and cooling zones disposed successively along its length with driven roller control means at the outlet of the crimping zone operable to control the pressure to which the core is exposed in such zone above the feed rolls and wherein the core above such roller control means is exposed to low frictional drag in passing through the heating and cooling zones of the stuffer crimper chamber.

Also an object of the invention is to provide a stuffer crimper of the above type which is particularly adapted for crimping heavy denier yarns such as employed in carpet manufacture.

A more general object of this invention is in providing a yarn crimping apparatus of the stuffer crimper type having novel and improved characteristics.

In general, a preferred embodiment of the invention for crimping yarn provides a yarn core confining chamber with crimping, heating and cooling zones disposed successively along its length and yarn feed rolls mounted at the inlet to such chamber to feed yarn into the crimping zone and form a core of yarn within the chamber. Roller means mounted to rotate parallel to the axes of the feed rolls are disposed at the juncture of the crimping and heating zones with such roller means having a core gripping surfacing projecting into the chamber and being driven at a speed related to the yarn feed speed so as to independently control the pressure on the core within the crimping zone relative to the pressure to which the core is subjected to in the heating and cooling zones of the chamber.

The above-mentioned roller means may be driven at different speeds relative to the yarn feed speed to thereby control and vary as desired the back pressure to which the yarn core is subjected in the crimping zone disposed immediately adjacent the feed rolls. By selecting different driving speeds for the control roller means and thereby obtaining different back pressures on the crimped yarn core in the crimping zone, it has been determined that for a given yarn feed speed, as determined by the speed of the feed rolls, the leg length of the crimp in the yarn can be shortened or lengthened with a degree of predictability such that a desired final crimped yarn product can be obtained by simply setting the proper drive speed of the control roller means which rotate parallel to the axes of the feed rolls.

As a further feature of the driven control roller means, the core gripping surfacing thereon may advantageously consist of gear-like teeth on the circumference of the roller means. This surfacing is beneficial in assuring positive and non-slipping interengagement between the roller means and the crimped yarn core which thereby achieves the desired positive control of the back pressure to which the yarn is exposed when it enters the crimping zone under the introducing force imparted to the yarn as it passes from the bite of the feed rolls.

A further feature of the invention follows from utilization of the above-described back pressure control in the crimping zone achieved by the positively driven roller means combined with provision of a relatively low friction chamber construction where the chamber of the stuffer crimper extends through the heating and cooling zones. Thereby, the frictional resistance to the crimped yarn core moving through the heating and cooling zones, beyond the driven roller control means, is reduced. With this reduced frictional back pressure, control and variation of the pressure on the core moving through the heating and cooling zones may also be independently controlled and varied by utilizing a core retarding means such as a weight biased rake choke where the tines of the rake choke extend into a parallel bar cage, forming the chamber for confining the yarn core within the cooling zone, and engage the core to set up the desired back pressure so that the particular sharp crimp angle for the yarn to be produced will be obtained and set as the core passes through the heating and cooling zones.

Various other objects and details of construction will be apparent as the nature of the invention is more fully disclosed. Such invention will be better understood from the following description, taken in connection with the accompanying drawing in which a specific embodiment has been set forth for purposes of illustration.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic perspective view, with certain parts shown in exploded relation, of the stuffer crimper apparatus of the instant invention; and

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1 showing the relationship of the pair of driven control rollers to the chamber at the junction of the crimping and heating zones.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT n FIG. 1 of the drawing, the yarn crimping apparatus in the form of a stuffer crimper is shown in somewhat diagrammatic form in relation to the related components employed in supplying yarn to the stufier crimper and winding up the crimped yarn withdrawn from the stuffer crimper. Thus, description will be given as to the general path for the yarn in moving through the equipment which, of course, includes as the principal yarn treating component the stuffer crimper 10.

A suitable yarn supply 12 is provided from which the yarn Y is drawn through an appropriate tension gate 14 and then passes over the guide 16 of a yarn traverse 18. The guide 16 shuttles back and forth under control of rotating traverse 18 to distribute the yarn back and forth across the length of the bite of the feed rolls 20 of the stufi'er crimper l0.

As is conventional in stuffer crimpers, the feed rolls 20 are geared together to operate at the same speed. As shown on FIG. 1, the feed rolls 20 are driven by an appropriate motor 22. Also as previously known, the traverse 18 is driven as by belt 24 from the drive shaft of motor 22 so that the traversing movements of yarn guide 16 and feed of the yarn back and forth along the length of the bite of feed rolls 20 is accomplished in relation to the yarn feeding speed of the feed rolls.

As the yarn Y passes between the bite of feed rolls 20, it enters into the crimping area 26 of the chamber and is therein crimped into a core of yarn within this area of the stuffer crimper chamber.

In the illustrated embodiment, the crimping zone of the chamber is formed by the walls of nose pieces 28 and 30. These pieces are shown separated on FIG. I to better illustrate the interior of the crimping zone. The two nose pieces, when assembled, provide a saddle which closely conforms with the surfaces of the feed rolls 20 to receive the yarn as fed through the bite of the feed rolls to form the crimped yarn core. The side walls of the nose pieces 28 and 30 extend from the bite of the feed rolls and saddle up to the control roller means, hereinafter described, in the manner shown on FIG. 2. The crimping zone extends upwardly, including area 26, from the bite of feed rolls 20 through the portion where the core of crimped yarn is confined within the walls of nose pieces 28 and 30 to the control roller means, this crimping zone being identified A as shown on FIG. 1 of the drawing.

Adjacent the upper end of the nose pieces 28 and 30 are a pair of rollers 32 and 34, appropriately journaled to rotate about axes parallel to each other and also parallel to the axes of rotation of the feed rolls 20. The parallelism of the axes of rollers 32 and 34 to the axes of the feed rolls 20 is of importance in relation to the action of yarn traverse 18 relative to feed rolls 20. As described above, the yarn traverse lays the yarn back and forth across the length of the bite of the feed rolls 20. By having the rollers 32 and 34 parallel to the feed rollers, these rollers apply a uniform back pressure through the crimped yarn core across the entire bite of the feed rolls.

These rollers 32 and 34 provide the control roller means and are mounted such that the periphery thereof project into the chamber from opposite sides at the upper end of the crimping zone A. Above the rollers 32 and 34, the heating zone of the stuffer crimper chamber starts and above the heating zone is the cooling zone in the embodiment illustrated.

The rollers 32 and 34 have the shafts on which they are mounted interconnected by gears 36 so that the two rollers will be rotated simultaneously. As shown, the roller 32 has its shaft driven, through belt 38, by the driving shaft of motor 22 which also drives the feed rolls 20. Thus, rollers 32 and 34 are driven at a speed related to the rotative speed of the feed rolls 20 and consequently, related to the yarn feed speed as it enters the crimping area 26 from the bite of rolls 20.

In the embodiment, as illustrated, each of the rollers 32 and 34 has a surface formed thereon such that they will effectively grip the core of crimped yarn as it moves upwardly from the crimping zone within nose pieces 28 and 30 to the position of rollers 32 and 34. In the preferred embodiment, these rollers 32 and 34 have the core gripping surfacing provided by gear-like teeth formed on the periphery of and extending longitudinally of each of these rollers. The core gripping surfacing in the form of these gear-like teeth and the relationship of the rollers 32 and 34 is best shown in the sectional view of FIG. 2.

By reason of the axes of the rollers 32 and 34 being parallel to the axes of the feed rolls 20, the core in the rectangular stuffer crimper chamber, as illustrated, is effectively controlled as to the pressure imparted thereto within the crimping zone A. Thus, this pressure in the crimping zone is isolated or made independent of that pressure which may be desired or may exist in the heating and cooling zones of the chamber disposed above the location of rollers 32 and 34. Likewise by changing the driven speed of rollers 32 and 34, the amount of back pressure applied on the core below the rollers may be increased or decreased. By so increasing or decreasing this back pressure, the leg length of the crimps produced into the yarn, as it is introduced to the inlet of the crimping chamber, can be effectively increased or decreased. In any event, by the driven control roller means of this invention, the pressure applied to the yarn core in the crimping zone is isolated from whatever pressure exists, be it frictional resistance pressure or introduced back pressure, in the heating and cooling zones and this latter pressure will be isolated from the crimping zone pressure.

In the preferred embodiment illustrated, the control rollers are provided with gear teeth on their periphery and along their length. These teeth, although projecting into the chamber of the stuffer crimper at the upper end of the crimping zone but still closely adjacent the bite of the feed rolls, are spaced as shown in FIG. 2 such that the core in moving upwardly through the chamber is gripped but not unduly distorted or disturbed. The objective of the control rollers 32 and 34 is to use the driving speed of these rollers to set the back pressure on the core in the crimping chamber in relation to the rate of yarn fed by rolls 20 into the crimping zone and also use this driving force on the rollers 32 and 34 to provide any force necessary to grip and move the core onwardly through the succeeding heating and cooling zones of the chamber.

Whereas the gear-like teeth provide the preferred core gripping surfacing on the rollers, it is to be understood that other difi'erent types of surfacing can be employed. By appropriately spacing the rollers to alter the extent to which the core gripping surfacing thereof projects into the chamber, different surfacing than gear teeth, such as grooves, roughening, or other gripping surface, may be employed. The important objective is that the surfacing be proper for the particular yarn, pressure conditions of the core and other parameters in operation of the stuffer crimper. Thus, the core gripping surfacing on the rollers must properly grip the core to give the controlled back pressure in the crimping zone and still feed the core on through the heating and cooling zones with the desired pressure in these latter two zones.

Although a pair of rollers each having core gripping surfacing on the periphery thereof have been illustrated in the fonn of rollers 32 and 34, it is to be understood that under some conditions a single roller with appropriate core gripping surfacing on its perimeter may be employed. In this event, the core will be gripped with the pressure in the crimping zone and pressure in the heating and cooling zones independently controlled by this one roller controlling core movement by pressing the core against the wall of the crimping zone portion of the chamber opposite the location of such single roller.

It also will be understood that as illustrated where the rollers 32 and 34 are intergeared to rotate together and are then driven from the single power source of motor 22, which also drives feed rollers 20, the rollers 32 and 34 may be driven by a separate power source than that used to drive the feed rolls 20. Obviously, the driving speed of rollers 32 and 34 is desirably related to the rate of yarn feed which is determined by the rotative speed of feed rolls 20 and thus to get optimum results in control of pressure in the crimping zone of the chamber the rollers 32 and 34 are advantageously driven at a speed related to that of the feed rolls.

Particular attention is drawn to the ample spacing surrounding the rollers 32 and 34, as shown in FIG. 2,

where they are mounted to project inwardly of the inner walls of the nose pieces 28 and 30. The provision of ample space around the rollers, such as shown on FIG. 2 of the drawing, is important in that it better facilitates movement of die crimped yarn core upwardly out of the crimping area 26 and on into the heating zone. Where a close tolerance is provided at the point where the walls of the chamber approach the perimeter of the rollers 32 and 34, it has been found that the yarn filaments tend to get snarled and broken by becoming pinched between the teeth on the rollers and the adjacent stationary wall portions.

Above the position where the core gripping surfacing of the rollers 32 and 34 projects into the chamber of the stufier crimper 10, the core of crimped yarn passes into the heating zone. Thus, the driven control roller means is disposed at the juncture of the crimping zone and the heating zone. Beyond the heating zone the core moves into the cooling zone. In the embodiment as illustrated, the passage of the core within the heating and cooling zones comprises a length of the chamber designated by B on FIG. 1.

The heating zone portion of the stuffer crimper chamber is provided by a cage chamber construction having rail means formed with parallel inwardly projecting ribs 40 disposed around the periphery of the chamber. In the heating zone, this cage and the ribs 40 are formed on the interior of the half sections 42 and 44, shown in exploded relation on FIG. 1 to better illustrate the interior of the chamber in the heating zone. Of course, the half sections 42 and 44 will each be provided with appropriate heating means (not shown) to elevate the temperature of these sections and thereby produce the required temperature for treatment of the crimped yarn core therewithin. The ribs 40 forming the cage construction of the chamber in the heating zone serve to reduce the area of engagement of the chamber with the yarn core in this zone and thereby reduce or minimize the frictional drag on the core as it moves upwardly through the heating zone.

Above the heating zone formed within the sections 42 and 44, the cage chamber continues with rail means being provided by parallel bars 46 disposed around the periphery of the chamber in the portion of the chamber which forms the cooling zone. Thus, the inwardly projecting surfaces of the bar cage formed by bars 46 provide rail means as continuations of the individual ribs 40 in the sections 42 and 44 of the heating zone chamber portion and the core of crimped yarn is conlined and guided onwardly from the heating zone into the cooling zone. The parallel bars 46 like the ribs 40 in the heating zone provide rail means offering minimal frictional resistance to passage of the core through the cooling zone.

The pressure imparted to the core is to an extent dependent upon the frictional resistance which the core encounters in moving along the rail means within the heating and cooling zones. Of course, the pressure within the crimping zone A is isolated from the pressure to which the core is exposed to in the heating and cooling zones by the driven control roller means provided by toothed rollers 32 and 34 in the illustrated embodiment. However, it is desirable to apply a controlled back pressure to the core in the heating and cooling zone so that the desired setting of a sharp crimp angle in the yarn filaments can be achieved. Accordingly, a core retarding means, in the form of a rake element 48 having tines 50, is pivotally mounted so that the tines 50 can be urged inwardly between the parallel bars 46 of the cooling zone portion of the chamber with the tines engaging the yarn core and thereby establishing resistance to movement of the core through the cooling zone and consequently establishing the back pressure existing on the core within the heating and cooling zones above the driven control rollers 32 and 34. The rake element 48 may have a suitable arm 52 extending therefrom with a weight 54 suspended from the outer end thereof. Of course, variation in the amount of the weight 54 will determine the extent to which the tines 50 of the rake element 48 are biased inwardly against the movement of the yarn core within the cooling chamber and consequently, determine the back pressure to which the yarn core is subjected to in passing through the heating and cooling zones.

A further advantage flows from providing the driven control rollers 32 and 34 in relation to moving the crimped yarn core through the length of the chamber designated B on FIG. I encompassing the heating and cooling zones. These rollers independently advance the core of crimped yarn through the zone B. in so doing, deposits that may build up on the walls of the chamber and the length of the chamber zone B do not significantly effect the back pressure on the yarn core in crimping zone A. Consequently, there is more flexibility in determining the length of the chamber that can be used and the chamber itself does not have to be cleaned as often when driven control rollers such as 32 and 34 are used.

As illustrated, a pair of core retarding means involving rake elements 48, one being mounted on each side of the bar cage forming the cooling zone portion of the chamber are illustrated in H0. 1. The second core retarding rake element and associated parts are shown in exploded fashion to better illustrate the relationship of the first rake element to the bar cage of the cooling zone.

Beyond the core retarding means formed by the rake elements 48 on opposed sides of the cooling zone bar cage, the core continues through the bar cage to a sensing frame 56 which is pivotally mounted at 58 and rests on the end of the core of crimped yarn. The frame is connected to control a rheostat 60 which is to control the yarn winder speed, depending upon the varying height of the upper end of the crimped yarn core in the bar cage cooling zone of the stuffer crimper chamber. The winder withdraws the crimped yarn from the end of the core and between the parallel bars of the sensing frame 56.

in being withdrawn from the core of crimped yarn, the yarn passes out of the bar cage of the cooling zone through guide eyelets 62 and 64, and then over a traverse guide 66 which lays the yarn in windings on the package 68. The package is mounted to be rotatably driven by drive motor 70. As shown, the speed of drive motor 70 is controlled by the setting of rheostat 60 so that the position of the end of the crimped yarn core within the cooling zone will be maintained relatively constant, with the package 68 operating faster or slower to withdraw the crimped yarn as needed to maintain such constant position of the end of the crimped yarn core.

it is to be understood that the form and embodiment of the invention herein shown and described is to be taken only as a preferred representation of the invention and that various changes and modifications in the arrangement of the components, parts, units, etc. may be resorted to without departing from the spirit or scope of the appended claims.

What is claimed is: a

l. Yarn crimping apparatus comprising:

a stuffer crimper having a yarn core confining chamber defining crimping, heating and cooling zones disposed successively along the length of said chamber;

yarn feed rolls mounted at the inlet to said chamber to feed yarn into said crimping zone to produce a core of crimped yarn within said chamber;

roller means mounted to rotate parallel to the axes of said feed rolls and disposed at the juncture of said crimping and heating zones to independently control thepressure on the core within said crimping zone relative to the pressure on the core in said heating and cooling zones of said chamber, said roller means having core gripping surfacing which projects into said chamber at said juncture; and

means for positively rotatably driving said roller means independently of the pressure exerted thereon by the core within said crimping zone, said driving means being operable to drive said roller means at a speed related to the yarn feed speed as determined by the speed of said feed rolls.

2. Yarn crimping apparatus as recited in claim 1 wherein said roller means comprises a pair of rollers with the core gripping surfacing of said rollers projecting inwardly from opposite sides of said chamber at said juncture.

3. Yarn crimping apparatus as recited in claim I wherein said core gripping surfacing consists of gearlike teeth on said roller means.

4. Yarn crimping apparatus as recited in claim I wherein said roller means and said feed rolls are driven by a single source at speeds proportional to one another.

5. Yarn crimping apparatus as recited in claim 1 wherein said roller means comprises a pair of rollers disposed on opposite sides of said chamber at said juncture of said crimping and heating zones with the core gripping surfacing of each roller projecting inwardly of said chamber, and said pair of rollers are driven at the same speed.

6. Yarn crimping apparatus as recited in claim 5 wherein said pair of rollers are connected by gearing externally of said chamber to rotate simultaneously.

7. Yarn crimping apparatus as recited in claim 5 wherein each of said pair of rollers has gear-like teeth on the exterior thereof to provide said core gripping surfacing.

8. Yarn crimping apparatus as recited in claim I wherein core retarding means is provided to engage the yarn core within said chamber in said cooling zone to control the pressure on the core within said heating and cooling zones of said chamber but beyond the position of said roller means.

lOoOlZ 0165 9. Yarn crimping apparatus as recited in claim 8 wherein the cooling zone of said chamber is formed by a parallel bar cage confining the yarn core therewithin, said core retarding means comprises spaced tines extending inwardly of the bars of said cage to engage the yarn core, and said tines are adjustably biased against the core to control the pressure on the core in the heating and cooling zones of said chamber.

10. Yarn crimping apparatus comprising:

a stuffer crimper having a yarn core confining chamber defining crimping, heating and cooling zones disposed successively along the length of said chamber;

yarn feed rolls mounted at the inlet to said chamber to feed yarn into said crimping zone to produce a core of crimped yarn within said chamber;

wall means forming the crimping zone of said chamber;

a cage having a set of spaced parallel inwardly projecting rail means disposed around the periphery of said chamber with the inner surfaces of said rail means forming a continuation of said wall means of the crimping zone, said rail means extending all throughout the length of the heating and cooling zones of said chamber for confining and guiding the yam core therethrough;

roller means mounted to rotate parallel to the axes of said feed rolls and disposed at the juncture of said crimping and heating zones to independently control the pressure on the core within said crimping zones relative to the pressure on the core in said heating and cooling zones of said chamber, said roller means having core gripping surfacing which projects into said chamber at said juncture; and means for positively rotatably driving said roller means independently of the pressure exerted thereon by the core within said crimping zone, said driving means being operable to drive said roller means at a speed related to the yarn feed speed as determined by the speed of said feed rolls.

ll. Yarn crimping apparatus as recited in claim 10 wherein said wall means forming the crimping zone of said chamber have the side walls diverging from the bite of said feed rolls to the mounting position of said roller means.

I i i I t 

1. Yarn crimping apparatus comprising: a stuffer crimper having a yarn core confining chamber defining crimping, heating and cooling zones disposed successively along the length of said chamber; yarn feed rolls mounted at the inlet to said chamber to feed yarn into said crimping zone to produce a core of crimped yarn within said chamber; roller means mounted to rotate parallel to the axes of said feed rolls and disposed at the juncture of said crimping and heating zones to independently control the pressure on the core within said crimping zone relative to the pressure on the core in said heating and cooling zones of said chamber, said roller means having core gripping surfacing which projects into said chamber at said juncture; and means for positively rotatably driving said roller means independently of the pressure exerted thereon by the core within said crimping zone, said driving means being operable to drive said roller means at a speed related to the yarn feed speed as determined by the speed of said feed rolls.
 2. Yarn crimping apparatus as recited in claim 1 wherein said roller means comprises a pair of rollers with the core gripping surfacing of said rollers projecting inwardly from opposite sides of said chamber at said juncture.
 3. Yarn crimping apparatus as recited in claim 1 wherein said core gripping surfacing consists of gear-like teeth on said roller means.
 4. Yarn crimping apparatus as recited in claim 1 wherein said roller means and said feed rolls are driven by a single source at speeds proportional to one another.
 5. Yarn crimping apparatus as recited in claim 1 wherein said roller means comprises a pair of rollers disposed on opposite sides of said chamber at said juncture of said crimping and heating zones with the core gripping surfacing of each roller projecting inwardly of said chamber, and said pair of rollers are driven at the same speed.
 6. Yarn crimping apparatus as recited in claim 5 wherein said pair of rollers are connected by gearing externally of said chamber to rotate simultaneously.
 7. Yarn crimping apparatus as recited in claim 5 wherein each of said pair of rollers has gear-like teeth on the exterior thereof to provide said core gripping surfacing.
 8. Yarn crimping apparatus as recited in claim 1 wherein core retarding means is provided to engage the yarn core within said chamber in said cooling zone to control the pressure on the core within said heating and cooling zones of said chamber but beyond the position of said roller means.
 9. Yarn crimping apparatus as recited in claim 8 wherein the cooling zone of said chamber is formed by a parallel bar cage confining the yarn core therewithin, said core retarding means comprises spaced tines extending inwardly of the bars of said cage to engage the yarn core, and said tines are adjustably biased against the core to control the pressure on the core in the heating and cooling zones Of said chamber.
 10. Yarn crimping apparatus comprising: a stuffer crimper having a yarn core confining chamber defining crimping, heating and cooling zones disposed successively along the length of said chamber; yarn feed rolls mounted at the inlet to said chamber to feed yarn into said crimping zone to produce a core of crimped yarn within said chamber; wall means forming the crimping zone of said chamber; a cage having a set of spaced parallel inwardly projecting rail means disposed around the periphery of said chamber with the inner surfaces of said rail means forming a continuation of said wall means of the crimping zone, said rail means extending throughout the length of the heating and cooling zones of said chamber for confining and guiding the yarn core therethrough; roller means mounted to rotate parallel to the axes of said feed rolls and disposed at the juncture of said crimping and heating zones to independently control the pressure on the core within said crimping zones relative to the pressure on the core in said heating and cooling zones of said chamber, said roller means having core gripping surfacing which projects into said chamber at said juncture; and means for positively rotatably driving said roller means independently of the pressure exerted thereon by the core within said crimping zone, said driving means being operable to drive said roller means at a speed related to the yarn feed speed as determined by the speed of said feed rolls.
 11. Yarn crimping apparatus as recited in claim 10 wherein said wall means forming the crimping zone of said chamber have the side walls diverging from the bite of said feed rolls to the mounting position of said roller means. 